Preparation of nanosized copper (I) compounds

ABSTRACT

A method of making nanosized copper (I) compounds, in particular, copper (I) halides, pseudohalides, and cyanocuprate complexes, in reverse micelles or microemulsions is disclosed herein. The method of the invention comprises (a) dissolving a copper (II) compound in the polar phase of a first reverse micelle or microemulsion, (b) dissolving a copper (II) to copper (I) reducing agent or a pseudohalide salt in the polar phase of a second sample of the same reverse micelle or microemulsion, (c) mixing the two reverse micelle/microemulsions samples to form nanometer sized copper (I) compounds and (d) recovering said nanometer sized copper (I) compounds. The present invention is also directed to the resultant nanosized copper (I) compounds, such as copper (I) chloride, copper (I) cyanide, and potassium cyanocuprate complexes having an average particle size of about 0.1 to 600 nanometers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/413,754 filed Apr. 16, 2003, now U.S. Pat. No. 7,700,796, whichclaims the priority of U.S. Provisional Application No. 60/375,957,filed Apr. 25, 2002, entitled PREPARATION OF NANOSIZED COPPER (I)COMPOUNDS, both of said applications being incorporated by referenceherein in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a method of making nanosized copper(I) compounds and the resultant nanosized copper (I) compounds. Inparticular, the present invention is directed to a method of makingnanosized copper (I) chloride, copper (I) cyanide, and cyanocupratecomplexes.

2. Description of Related Art

Nanometer sized particles have diameters in the range from about 1nanometer (10⁻⁹ meter) to about 100 nanometers (10⁻⁷ meter). Thesematerials are also described in the art as nanostructured,nanocrystalline, nanosized, nanoparticulate, nanoscale, ultrafine, orsuperfine. Their structures and high surface to volume ratio make themdesirable in catalytic, electronic, magnetic, and coating (pigment)applications. Various physical and chemical methods have been disclosedin the art for their preparation.

Nanosized copper (I) chloride is desired for its nonlinear opticalproperties and its utility in optoelectronics. There is a need fornanosized CuCl to satisfy the many laser and other applications in thisfield. The known art (see T. Ito, Seramikkusu, 27:508-514 (1992); A.Onushchenko, et al., J. Non-Crystalline Solids, 196:73-78 (1996); T. Itoet al., in Mesoscopic Materials and Clusters (T. Arai, Editor),Springer, Berlin, (1999), pp, 31-46, discloses synthesis of nanosizedCuCl embedded in glass, alkali halide, and polymer matrices. However,the synthetic methods used are not suited to catalytic applications orto the isolation and recovery of nanocrystalline CuCl.

Copper (I) cyanide, CuCN, is a copper source for yttrium-barium-copperoxide superconductors, copper plating baths, and as a catalyst forGrignard and other alkylation reactions. Solid cyanocuprates such asM[Cu(CN)₂], M[Cu₂(CN)₃], M₂[Cu(CN)₃] and M₃[Cu(CN)₄] where M is sodium,potassium, or other metal, are important in the recovery of copper fromores. They have infinite microporous frameworks, which have utility inmolecular sieves and catalysis.

It is known in the art to dissolve a soluble copper (II) compound in thepolar phase of a reverse micelle/microemulsion of defined polar phase tosurfactant molar ratio. A reducing agent (for example, NaBH₄ or N₂H₄) isdissolved in the polar phase of another sample of the same reversemicelle/microemulsion. Mixing the two samples leads to reduction of Cu(II) and formation of nanosized copper (I) oxide and/or nanosized coppermetal. Cu₂O with 5-10 nanometer particles was prepared in this way byZou, et al. (Chinese Science Bulletin, 39:14-18(1994)). Lisecki, et al.(J. Physical Chemistry, 100:4160-4166 (1996)) disclosed the control ofcopper particle size and dispersity by control of water/surfactant molarratio. Nanoparticles 2-10 nanometers were obtained at molar ratios,1-10. Qi, et al. (J. Colloid and Interface Science, 186:498-500 (1997))also prepared 5-15 nanometer copper particles in reverse micelles. M. P.Pileni (J. Physical Chemistry, 97:6961-6973(1993)) has reviewed thesubject. In general, use of sodium borohydride or hydrazine does notallow careful, selective reduction to a nanosized copper (I) productfrom the copper (II) precursor, but rather complete reduction tonanosized copper (0) metal.

U.S. Pat. No. 5,770,172 to Linehan et al. issued on Jun. 23, 1998,discloses a process for producing nanometer-sized metal compoundscomprising forming a reverse micelle or reverse microemulsion systemcomprising a polar fluid in a non-polar or low-polarity fluid. Again, asin the references cited above, the types of reducing agents used, i.e.,phosphates, hydrazines, sodium borohydride, do not allow selectivereduction to the copper (I) product from the copper (II) precursor. Thereduction proceeds to the elemental metal.

Although it is known that the reduction of CuCl₂ to CuCl can be effectedby ascorbic acid (E. Stathis, Chemistry & Industry (London), 1958, p633), by sulfites and reducing sugars (G. Fowles, The School ScienceReview, 44(1963) pp 692-694), and by phosphorous acid (R. N. Keller,Inorganic Syntheses, Vol. II, 1946, pp 1-4), there are no known previousapplications of these chemistries to the synthesis of nanosized CuCl.

U.S. patent application Ser. No. 09/974,503 filed Oct. 9, 2001 teachesthe preparation of nanosized CuCl by reaction of nanosized Cu₂O with HClin hydrocarbon solvents, or in a gas-solid environment. Reduction ofCu(II) is not essential since the nanosized Cu₂O can be formed by anyphysical or chemical method available.

Notwithstanding the state of the prior art, it would be desirable toprovide a method of making nanosized copper (I) compounds wherein thereis a controlled and selective reduction from the copper (II) precursorto the copper (I) product and the resultant nanosized copper (I)compounds.

SUMMARY OF THE INVENTION

The present invention provides a method and process for producingnanosized copper (I) compounds, particularly CuCl, CuCN, andcyanocuprate complexes, in the range from about 0.1-600 nanometers. Themethod and process for CuCl comprise:

(a) dissolving a copper (II) compound in the polar phase of a reversemicelle or microemulsion dispersed within a non-polar continuous phasein the presence of surfactants or emulsifiers,

(b) dissolving a reducing agent in the polar phase of another sample ofthe same reverse micelle or microemulsion,

(c) mixing the two reverse micelles/microemulsions to form nanometersized CuCl, and

(d) recovering said nanometer sized CuCl.

Nanosized CuCl made by the instant method and process is useful incatalytic and non-linear optical applications.

For nanosized CuCN, the method and process comprise:

(a) dissolving a copper (II) compound in the polar phase of a reversemicelle or microemulsion dispersed within a non-polar continuous phasein the presence of surfactants or emulsifiers,

(b) dissolving a soluble cyanide in the polar phase of another sample ofthe same reverse micelle or microemulsion,

(c) adding the cyanide-containing reverse micelle/microemulsion to thecopper (II)-containing one so that the molar ratio of cyanide to copperin the mixture remains ≦2,

(d) optionally, heating the reaction mixture to decompose any Cu(CN)₂and/or Cu[Cu(CN)₂]₂ to nanosized CuCN, and

(e) recovering said nanosized CuCN.

In another aspect, the present invention is directed to the formation ofnanosized cyanocuprate complexes of general formulae, M[Cu(CN)₂],M[Cu₂(CN)₃], M₂[Cu(CN)₃], and M₃[Cu(CN)₄], where M is Li, Na, K, or Cs.For these compounds, the method and process include:

(a) dissolving a copper (II) compound in the polar phase of a reversemicelle or microemulsion dispersed within a non-polar continuous phasein the presence of surfactants or emulsifiers,

(b) dissolving a soluble cyanide in the polar phase of another sample ofthe same reverse micelle or microemulsion,

(c) adding the copper (II)-containing reverse micelle/microemulsion tothe cyanide-containing one so that there exists a molar excess ofcyanide relative to copper in the mixture to form, initially, nanosizedCu[Cu(CN)₂]₂ and/or Cu(CN)₂,

(d) reacting Cu[Cu(CN)₂]₂ and/or Cu(CN)₂ with excess cyanide, and,optionally, heating to form nanosized cyanocuprates, and

(e) recovering said nanosized cyanocuprates.

More particularly, the present invention is directed to a method ofpreparing a nanosized copper (I) compound comprising the steps of:

providing a first microemulsion having a discontinuous polar phasecomprising a copper (II) precursor;

providing a second microemulsion having a discontinuous polar phasecomprising a copper (II) to copper (I) reducing agent or a correspondingsalt of a pseudohalide;

combining the first and second microemulsions in a reaction mixture; and

separating the nanosized copper (I) compound from the reaction mixture.

In another aspect, the present invention is directed to a method ofpreparing nanosized copper (I) chloride comprising the steps of

providing a first microemulsion having a polar phase to surfactant molarratio of less than about 30 comprising

-   -   a low or non-polar continuous phase comprising a surfactant, and        a discontinuous polar phase comprising a copper (II) chloride        where the discontinuous polar phase comprises nanosized droplets        of the copper (II) chloride;

providing a second microemulsion having a polar phase to surfactantmolar ratio of less than about 30 comprising

-   -   a low or non-polar continuous phase comprising a surfactant, and    -   a discontinuous polar phase comprising a reducing agent where        the discontinuous polar phase comprises nanosized droplets of        the reducing agent;

combining the first and second microemulsions into a reaction mixture;and

collecting the nanosized copper (I) chloride from the admixture.

In yet another aspect, the present invention is directed to a method ofpreparing nanosized copper (I) cyanide comprising the steps of:

providing a first microemulsion having a polar phase to surfactant molarratio of less than about 30 comprising

-   -   a low or non-polar continuous phase comprising a surfactant, and    -   a discontinuous polar phase comprising a copper (II) precursor        where the discontinuous polar phase comprises nanosized droplets        of the copper (II) precursor;

providing a second microemulsion having a polar phase to surfactantmolar ratio of less than about 30 comprising

-   -   a low or non-polar continuous phase comprising a surfactant, and    -   a discontinuous polar phase comprising a cyanide salt soluble in        the polar phase where the discontinuous polar phase comprises        nanosized droplets of the cyanide salt;

combining the first and second microemulsions to form Cu(CN)₂ and/orCu[Cu(CN)₂]₂;

thermally decomposing the Cu(CN)₂ and/or Cu[Cu(CN)₂]₂ to copper (I)cyanide; and

collecting the nanosized copper (I) cyanide having an average particlesize of less than 100 nanometers.

In still another aspect, the present invention is directed to a methodof preparing nanosized cyanocuprate complexes comprising the steps of:

providing a first microemulsion having a polar phase to surfactant molarratio of less than about 30 comprising

-   -   a low or non-polar continuous phase comprising a surfactant, and    -   a discontinuous polar phase comprising a copper (II) precursor        where the discontinuous polar phase comprises nanosized droplets        of the copper (II) precursor;

providing a second microemulsion having a polar phase to surfactantmolar ratio of less than about 30 comprising

-   -   a low or non-polar continuous phase comprising a surfactant, and    -   a discontinuous polar phase comprising a cyanide salt soluble in        the polar phase where the discontinuous polar phase comprises        nanosized droplets of the cyanide salt;

combining the first and second microemulsions into a reaction mixturewhere a CN⁻/Cu(I) molar ratio is greater than 1; and

collecting the nanosized cyanocuprate complexes from the admixture.

In a further aspect, the present invention is directed to a method ofpreparing nanosized copper (I) chloride comprising the steps of:

providing a first microemulsion having a polar phase to surfactant molarratio of about 4 to about 20 comprising

-   -   a low or non-polar continuous phase comprising a surfactant and        a co-surfactant, and    -   a discontinuous polar phase comprising copper (II) chloride        where the discontinuous polar phase comprises nanosized droplets        of the copper (II) chloride;

providing a second microemulsion having a polar phase to surfactantmolar ratio of about 4 to about 20 comprising

-   -   a low or non-polar continuous phase comprising a surfactant and        a co-surfactant, and    -   a discontinuous polar phase comprising a reducing agent soluble        in the polar phase selected from the group consisting of        ascorbic acid, ascorbic acid esters, salts of sulfurous acids,        salts of phosphorus acids, and reducing sugars, where the        discontinuous polar phase comprises nanosized droplets of the        reducing agent;

combining the first and second microemulsions to form copper (I)chloride; and

collecting the nanosized copper (I) chloride.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present invention is directed to a method of making nanosized copper(I) compounds, in particular, copper (I) halides, copper (I)pseudohalides, and pseudohalide cyanocuprate complexes, in reversemicelles or microemulsions. Reverse micelles and microemulsions areoptically clear, single phase dispersions of two immiscible liquidsstabilized by surfactants (emulsifiers). In the preparation of thesedispersions, a discontinuous polar phase (for example, water) isdispersed within a non-polar (or low polar) continuous phase (forexample, cyclohexane) in the presence of surfactants or emulsifiers. Thediscontinuous polar phase comprises nanosized droplets, whose dimensionsvary with the polar phase to surfactant molar ratio. Systems in whichthis ratio is less than fifteen are usually referred to as reversemicelles while microemulsions typically have polar phase to surfactantmolar ratios greater than fifteen. A microemulsion has also beendepicted as a bi-continuous region comprising a two-phase spongy-likenetwork in which the non-polar phase forms the cellular skeleton and thepolar phase fills the voids. The terms, “microemulsion” and “reversemicelles” are used interchangeably herein. The present invention is alsodirected to the resultant nanosized copper (I) compounds, such as copper(I) chloride, copper (I) cyanide, and potassium tetracyanocuprate (I)having an average particle size of from about 0.1 to about 600nanometers.

The method of the invention comprises (a) dissolving a copper (II)compound in the polar phase of a first reverse micelle or microemulsion,(b) dissolving a Cu(II) to Cu(I) reducing agent or a pseudohalide saltin the polar phase of a second sample of the same reverse micelle ormicroemulsion, (c) mixing the two reverse micelle/microemulsion samplesto form nanometer sized Cu (I) compounds and (d) recovering saidnanometer sized Cu (I) compounds.

Pseudohalides are anions, comprising more than two electronegativeatoms, which resemble halide ions in their chemical behavior. Examplesof such anions are cyanide (CN⁻), isocyanide (NC⁻), cyanate (OCN⁻),isocyanate (CNO⁻), thiocyanate (SCN⁻), and selenocyanate (SeCN⁻). Thus,sodium cyanide and potassium thiocyanate are examples of pseudohalidesalts that can be dissolved in the polar phase of the secondmicroemulsion. Copper (I) cyanide and copper (I) thiocyanate areexamples of copper pseudohalide compounds that can be prepared asnanosized materials according to the teachings of the instant invention.

Copper (II) Precursors

The copper (II) precursors useful in the present invention arecompounds, such as CuCl₂, CuBr₂, CuSO₄, Cu(NO₃)₂, Cu(OOCR)₂—where R ishydrogen, C_(n)H_(2n-1), phenyl or substituted phenyl, and n is 1 to 8inclusive—other copper (II) carboxylates, such as maleate, fumarate,citrate, and tartrate, copper (II) diketonates and copper (II)alkoxides, which are soluble in polar solvents and are reducible to acopper (I) compound. Most preferred are CuCl₂ and CuSO₁.

The copper (II) precursor can also be complex salts of the generalformulae MCuX₃ and MCuX₄, wherein M is an alkali metal, such as Li, Na,K, or Cs and X is a halide, such as Cl or Br. These complex salts areknown in the art to be formed by mixing solutions of the copper (II)halide and alkali metal halide in appropriate stoichiometricproportions. Analogous copper (I) complex salts are also known. Theyhave the general formulae MCuX₂, M₂CuX₃, and M₃CuX₄, wherein M and Xhave the same meanings as defined above.

The copper (I) halide-alkali metal halide complexes can be formed byreduction of the corresponding copper (II) complexes with metalliccopper. For example, KCuCl₂ can be obtained in the following way KCl(3.5-4.0 moles) and CuCl₂ (0.5-1.0 mole) are dissolved in one liter ofwater to form KCuCl₃ in excess KCl. Powdered copper metal (1.5-2.0moles) is then added and the mixture is stirred and heated to 80-100° C.for 3-5 hours. The resulting solution contains KCuCl₂ and can beemployed in forming the copper-bearing microemulsions of the presentinvention. Nanosized CuCN is produced when this emulsion is treated witha KCN-bearing microemulsion.

Reducing Agents & Pseudohalide Salts

The reducing agents of the instant invention are those capable ofconverting copper (II) to the copper (I) oxidation state. They must alsobe soluble in the polar phase of the reverse micelle/microemulsion.Suitable examples include ascorbic acid, its salts and esters, sulfurdioxide, sulfurous acid and sulfite salts, phosphorous acid and itssalts, iodide salts, cyanide salts, dialkyl sulfides, and reducingsugars (aldoses and ketoses), such as glucose and fructose. Preferredreductants are ascorbic acid, sulfurous acid, sulfite salts, phosphorousacid, and phosphite salts.

Pseudohalide salts, such as those of the alkali metals which are solublein polar solvents are suitable for use in the second reversemicelle/microemulsion sample. The pseudohalide salts are dissolved inthe nanosized droplets. They react with copper (II) when the twomicroemulsions are mixed to form transient or unstable, nanosized copper(II) salts, which decompose to yield the desired nanosized copper (I)compounds. Suitable pseudohalide salts are NaCN, KCN, KSCN, and NaOCN.Cyanide salts are preferred.

If the molar concentration of the pseudohalide anion in the reversemicelle/microemulsion exceeds that of copper, nanosized pseudohalidecuprate complexes can form. In these complexes, copper is still in the+1 oxidation state, but it is part of an anionic species. Examples ofthese anions are [Cu(CN₂]⁻, [Cu₂(CN)₃]⁻, [Cu(CN)₃]²⁻ and [Cu(CN)₄]³⁻.The anion that predominates depends on the CN/Cu(I) molar ratio in thereverse micelle/microemulsion. The CN/Cu(I) molar ratio is preferablegreater than about 1, more preferably about 1.5 to about 5.0.

Emulsion Systems

The reverse micelle and microemulsion systems useful in the presentinvention comprise a surfactant, preferably with a co-surfactant, a lowor non-polar phase, and a polar phase. The microemulsions, per se, areknown compositions when water is the polar phase. In some cases, theeffect of simple electrolytes on microemulsion stability has beenstudied, but these studies have not generally included copper (II)salts, or the pseudohalide salts and reducing agents relevant to theinstant invention. Additionally, these compositions have not beendisclosed previously for the preparation of nanosized copper (I)compounds. The table below summarizes the general composition of themicroemulsion systems.

Non-Polar Phase Polar Phase Surfactant Co-Surfactant Hydrocarbons WaterAlcohol Alcohols Ethoxylates Hydrocarbons Water Alkylpoly- Glycerolglucosides monoethers Hydrocarbons Water Alkylpoly- Alcohols glucosidesCyclic Silicones Water Siloxane- None Polyethers

As shown in the table, hydrocarbons can be employed as the low ornon-polar phase. Suitable examples are linear and branched alkanes, suchas hexane, isooctane, decane, and hexadecane; cycloparaffins, such ascyclohexane; and mixtures formed by exhaustive hydrogenation of highlyaromatic petroleum residues, alkylated benzenes, polyaromatichydrocarbons, petroleum distillates, and mineral oil. Hexane,cyclohexane, decane, nonylbenzene, NALKYLENE® 500 and WITCO CARNATION®70 are preferred. NALKYLENE 500 is a mixture of alkylated benzenes soldby Vista Chemical Company. WITCO CARNATION 70 is a mixture ofcycloparaffins sold by Crompton Corporation.

Cyclic siloxanes of the general formula (RR′SiO)_(n) where R and R′ areindependently alkyl, cycloalkyl, and aryl, such as, for example, methyl,ethyl, phenyl, phenethyl, and the like; and n is 3 to 20. Methyl is mostpreferred; and n is preferably 4 to 6.

The surfactants are molecules with distinct hydrophobic and hydrophilicregions. Depending on their chemical structures, the surfactants can benon-ionic, cationic, anionic, or zwitterionic. An example of a non-ionicsurfactant may be alkylphenolalkoxylates, such as TRITON® X-100,available from The Dow Chemical Company, Midland, Mich. Examples ofcationic surfactants include alkyl ammonium salts, such ashexadecyltrimethylammonium bromide. Anionic surfactants can includemetal salts of organosulfonates and organosulfosuccinates, such assodium dodecylsulfate (SDS) and sodium bis(2-ethylhexyl)sulfosuccinate(NaAOT), respectively. Examples of zwitterionic surfactants include3-(dimethyldodecyl-ammonium)propane sulfonate and cetyltrimethylammoniump-toluene sulfonate.

The hydrophobic part of the surfactant can be of various lengths, e.g.,8 to 20 carbon atoms, contain multiple bonds, or consist of two or morehydrocarbon chains. It can also contain organosiloxane groups and/ororganofluoro groups, and/or organofluorosiloxane groups. Preferredsurfactants useful for forming the reverse micelles and microemulsionsof the present invention include alcohol ethoxylates,alkylphenolethoxylates, silicone surfactants, and alkyl polyglycosides.

When the solubilization of water, or the polar phase, into the low ornon-polar phase by a non-ionic surfactant, such as TRITON X-100, ispoor, it can be enhanced by the addition of a co-surfactant, such as analcohol having from 5 to 10 carbon atoms. Preferred co-surfactants arepentanol, hexanol, and octanol, individually or in combination.Preferably, the weight ratio of co-surfactant to surfactant is about 1:5to 2:3.

Typically, the surfactant and co-surfactant, in a specific ratio, aremixed first to form a blend. The blend is then mixed with the low ornon-polar phase to form a homogenous blend solution. A preferable blendcontent in the solution is about 5 to about 30 vol. %. The low ornon-polar phase can be cyclohexane, hexane, hexadecane, isooctane,alkylated benzenes, polyaromatic hydrocarbons, linear and branchedparaffins, naphthenes, petroleum distillates, mineral oil, and/or linearor cyclic siloxanes.

Suitable polar solvents are water, monohydric, dihydric, and trihydricalcohols and organic nitriles, which have dipole moments greater thanone Debye and/or dielectric constants (also called relativepermittivity) greater than 6 at 20-25° C. Water is the preferred polarsolvent.

In the microemulsion, the size of the polar phase droplets (radius ofthe droplets “R_(w)” in nanometers) depends upon the polar phase tosurfactant molar ratio “w”. Thus, in sodium dioctylsulfosuccinatereverse micelles, the relationship between the radius of the dropletsand the polar phase to surfactant molar ratio is depicted by theformulae:R _(w)=0.15(w)(M. Pileni, Handbook of Surface and Colloid Chemistry, chapter 12, CRCPress, (1997)) andR _(w)=0.175(w)+1.5(P. Fletcher, et al., J. Chemical Society, Faraday Transactions, I, vol.83 (1987) 985-1006).

Preferably, the polar phase to surfactant molar ratio, w, is less thanabout 30, more preferably from about 4 to about 25, and most preferablyfrom about 6 to about 12. In some cases, the smaller the radius of thepolar phase droplets (that is, lower w), the smaller the resultantparticles of nanosized materials prepared in the microemulsion. However,there are published data (Pileni, loc. cit.) showing the opposite trend,viz a decrease in the size of the nanomaterial with increasing values ofw. Other publications (for example, U. Natrajan, et al., Langmuir, 12(1996) 2670-2678: T. Hatton, et al., Langmuir, 9 (1993) 1241-1253; andR. Bagwe, et al., Langmuir, 13 (1997) 6432-6138) report that the finalparticle size depends on variables other than the water to surfactantmolar ratio. These variables include the concentration of reactants, theinitial distribution of the reactant between the polar and nonpolarphases and the kinetics of solubilisate exchange between the waterdroplets. For nanosized calcium carbonate and molybdenum sulfide, it hasbeen reported (see K. Kandori, et al., J. Colloid Interface Sci., 122(1988) 78-82: E. Boakye, et al., J. Colloid Sci. 163 (1994) 120-120)that particle sizes increase with w up to a particular value and thenstay approximately constant or even decrease. Thus, there are no clearteachings in the art on the expected trends for the particle size valuesof nanosized copper (I) compounds as the water content of themicroemulsion is varied.

Mixing and Reaction Conditions

Vigorous mechanical stirring or ultrasonication is recommended duringthe mixing of the reactant microemulsions. One microemulsion can beadded to the other gradually, for example, from an addition funnel or asyringe pump, or rapidly all in one portion. The order and method ofaddition can influence the appearance of the reaction mixture and thesize and size distribution of the resultant nanosized product. In thepreparation of nanosized CuCl, slow addition of the reducing agentmicroemulsion to the copper (II)-containing microemulsion leadsinitially to clear, water-white reaction mixtures with no visible solidparticles. The nanosized CuCl nuclei remain in the water droplets and donot grow into larger visible crystals. When the reducing agent is addedrapidly in one portion to the copper (II), cloudiness and/orprecipitation of a white solid are observed immediately. This means thatnucleation and growth of CuCl have occurred simultaneously and thatlarger particles can be expected compared to the gradual method ofaddition.

Similar considerations apply to formation of copper (I) pseudohalidesand pseudohalide cuprates. However, in addition, formation of thepseudohalide cuprates depends on the order of addition of themicroemulsions. It is necessary that the copper (II)-containingmicroemulsion be added to the pseudohalide-containing one to maintain amolar ratio of pseudohalide ions to copper ions greater than 1,preferably greater than 2, during mixing and at the end of the transfer,to obtain the nanosized pseudohalide cuprate complexes.

EXAMPLES

The following examples illustrate the preferred embodiments of theinvention. They are not intended to limit the scope of the invention.Instead, they are presented to facilitate the practice of the inventionby those of ordinary skill in the art

LIST OF ABBREVIATIONS USED

ABBRE- VIATION MEANING ABBREVIATION MEANING g gram XRD X-ray diffractionnm nanometer HRSEM High resolution scanning electron microscopy μmmicron TEM Transmission electron (micrometer) microscopy D₄ [CH₃)₂SiO]₄FTIR Fourier transform infrared spectroscopy mL milliliter wWater/surfactant molar ratio d interplanar cm⁻¹ wavenumber spacing

Example 1

This Example illustrates the preparation of nanosized CuCl by reductionof CuCl₂ with ascorbic acid in the reverse micelle system comprisingTRITON X-100/n-hexanol/cyclohexane/water.

A blend of 7.86 grams of TRITON X-100 (F.W. 624) and 1.97 grams ofn-hexanol was first mixed having a weight ratio of co-surfactant tosurfactant of about 1:4. The blend was mixed with cyclohexane to form a100 mL blend/oil solution with 0.126 M TRITON X-100. An aqueous CuCl₂solution (2.0 M) was prepared by dissolving 0.541 gram of CuCl₂.2H₂O(F.W. 170.44) in 1.59 grams of water. The reverse micelles of aqueousCuCl₂ in cyclohexane were then obtained by adding the CuCl₂ solution tothe blend/oil solution. The water to surfactant molar ratio, w, was7.51.

The reverse micelles of aqueous ascorbic acid in cyclohexane wereprepared in the same manner by adding a solution of 0.418 gram ofascorbic acid (F.W. 176.12) in 1.59 grams of water (1.5 M) to 100 mL ofthe TRITON X-100/n-hexanol/cyclohexane blend/oil mixture to obtain amicroemulsion with w=7.01. The water of hydration in CuCl₂.2H₂O accountsfor the small difference in water/surfactant molar ratios between thetwo microemulsions.

Reduction of copper(II) to copper(I) occurred when the reverse micellesof ascorbic acid were added all in one portion to the reverse micellesof CuCl₂, while the latter was stirred mechanically in a large beakerunder nitrogen at room temperature. A white colloidal suspension wasformed. It was centrifuged for recovery of the solid.

XRD showed the white product to be CuCl. The most intense reflectionswere at d=3.109, 2.697, 1.910, and 1.631 Ångstroms. Both nanosized andmicronsized crystals were observed by HRSEM. The nanosized ones were500-600 nm.

Example 2

This Example illustrates the synthesis of nanosized K₃[Cu(CN)₄] in asilicone microemulsion.

The first microemulsion was prepared by adding, with mechanicalstirring, an aqueous solution of CuCl₂ to a mixture of cyclic D₄ (65 g)and SILWET® L-7622 (30 g). The CuCl₂ solution was made by dissolving1.704 g CuCl₂.2H₂O in 5 g deionized water. The second microemulsion wasprepared similarly with cyclic D₄ (65 g), SILWET L-7622 (30 g), KCN (1.3g) and deionized water (5 g). Based on the equivalent weight perpolyether pendant of the SILWET L-7622 surfactant, the water tosurfactant molar ratio, w, was 11.46.

The Cu(II)-silicone microemulsion was added all at once to thevigorously stirred KCN-silicone microemulsion in a large beaker in anitrogen atmosphere at room temperature. On mixing the twomicroemulsions, a dark brown solid was initially formed. When thereaction mixture was warmed to about 60° C., it changed to a light greencolor. The solid was separated by centrifugation and recovered bydecantation of the supernate. It was washed first with aqueous methanolto dissolve KCl and silicone surfactant, and later with dry methanolbefore drying at 100° C.

The XRD pattern of the solid was broad. It showed principal reflectionsat d spacings, 6.481, 5.891, 4.563, 4.152, 3.993, 3.846, and 3.592Ångstroms, in good agreement with standard powder file data forK₃[Cu(CN)₄]. The average particle size was 240 nm. FTIR spectroscopydisclosed a strong CN band at 2108 cm⁻¹ and the presence of the siliconesurfactant as a contaminant. Copper content was found to be 21.67 wt %.The calculated value for K₃[Cu(CN)₄] is 22.30 wt %.

Example 3

This Example illustrates the preparation of nanosized K₃[Cu(CN)₄] inreverse micelles/microemulsions with a water/surfactant molar ratio of8.57

The quantities of raw materials used are set forth in the followingtable:

Materials First Microemulsion Second Microemulsion TRITON X-100, g 8.08.0 n-Hexanol, g 2.0 2.0 Cyclohexane, g 70 70 CuCl₂•2H₂O, g 1.108 —Water, g 1.986 1.984 KCN, g — 0.842

When the second microemulsion was added all at once to the first, a darkbrown suspension of fine solids was produced. The color of the mixturebecame lighter during continued mixing at room temperature. On warmingto about 50 to 60° C., the mixture turned progressively yellow-brown,yellow-green, and finally light green. Heating was discontinued at 80°C., the boiling point of cyclohexane.

Solid products were recovered by centrifugation and washed at leastthree times with aqueous methanol before they were dried in an oven at100° C. FTIR spectroscopy showed a strong CN band at 2106 cm⁻¹ and thepresence of the surfactant as a contaminant in the recovered solid.Copper content was 18.83 wt % instead of the 22.30 wt % required by theformula. The XRD pattern was coincident with that obtained for theproduct of Example 3. HRSEM disclosed a bimodal distribution of cubiccrystals. The larger crystals were about one micrometer in size and thesmaller ones were about 200 to about 600 nanometers.

Example 4

This Example illustrates the synthesis of nanosized CuCl in a siliconemicroemulsion.

The first microemulsion was prepared by adding, with mechanicalstirring, an aqueous copper (II) chloride solution (1.729 g CuCl₂ in5.02 g water) to a mixture of cyclic D₄ (62.16 g) and SILWET L-7622(31.62 g). The second microemulsion was prepared similarly with cyclicD₄ (65.16 g), SILWET L-7622 (31.08 g), and an ascorbic acid solutionmade by dissolving 1.368 g of ascorbic acid in 5.07 g of deionizedwater. Based on the equivalent weight per polyether pendant of SILWETL-7622, the water to surfactant molar ratio was 11.07.

The silicone microemulsion containing ascorbic acid was added all atonce to the vigorously stirred, CuCl₂-containing silicone microemulsionin a large beaker in a nitrogen atmosphere at room temperature. Onmixing the two microemulsions, there was a visible increase in viscosityand the formation of finely divided white solid. The recovered solid hadthe same XRD pattern as a known sample of CuCl. HRSEM showed 25-30 nmround particles as well as 100-200 nm agglomerates of these particles.

Examples 5-8

These Examples illustrate the effect of rate of addition on theappearance of the microemulsion reaction mixture and on the particlesize of the nanosized solid obtained therefrom

The following tables set forth the compositions of the reactant pairs ofmicroemulsions and their respective water to surfactant molar ratios. InExamples 5 and 6, the ascorbic acid microemulsion (second microemulsionin the tables) was added dropwise from an addition funnel into themechanically stirred copper (II) chloride microemulsion (firstmicroemulsion in the tables). Rapid, manual addition of the ascorbicacid microemulsion to the copper (II) chloride emulsion was used inExamples 7 and 8. All reactions were performed in round bottom flaskswith provisions for a mechanical stirrer, addition funnel, and nitrogensparge tube.

Composition of Microemulsions of Example 5 (w = 7-7.5) Materials FirstMicroemulsion Second Microemulsion TRITON X-100, g 15.72 15.72n-Hexanol, g 3.94 3.94 Cyclohexane, g 140 140 CuCl₂•2H₂O, g 1.082 —Water, g 3.18 3.18 Ascorbic Acid, g — 0.866 Water/Surfactant Ratio 7.517.01

Composition of Microemulsions of Example 6 (w = 21-22.5) Materials FirstMicroemulsion Second Microemulsion TRITON X-100, g 7.86 7.86 n-Hexanol,g 1.97 1.97 Cyclohexane, g 70 70 CuCl₂•2H₂O, g 1.624 — Water, g 4.774.77 Ascorbic Acid, g — 1.299 Water/Surfactant Ratio 22.54 21.03

In the experiments, the blue color of Cu (II) was discharged graduallyduring the addition of the ascorbic acid microemulsion. The reactionmixtures were initially water white with no visible evidence of solidprecipitation. They were stored in opaque bottles because previousexperiments had shown that a yellow-brown coloration developed after 4-6weeks on exposure to ambient light. After one month's storage at roomtemperature, suspended white solid was visible in the product of Example5 and settled white solid in Example 6. The liquids remained water white

TEM was performed by evaporating a drop of each reaction mixturedirectly on the FORMVAR®/carbon grid of the instrument A minimum of 200particles was measured in each experiment. Average particle size of theCuCl in Example 5 (w=7-7.5) was 2.05±0.56 nm and in Example 6(w=21-22.5) was 2.98±0.90 nm

Composition of Microemulsions of Example 7 (w = 14-15) Materials FirstMicroemulsion Second Microemulsion TRITON X-100, g 7.86 7.86 n-Hexanol,g 1.97 1.97 Cyclohexane, g 70 70 CuCl₂•2H₂O, g 1.082 — Water, g 3.183.18 Ascorbic Acid, g — 0.966 Water/Surfactant Ratio 15.03 14.02

Composition of Microemulsions of Example 8 (w = 21-22.5) Materials FirstMicroemulsion Second Microemulsion TRITON X-100, g 7.86 7.86 n-Hexanol,g 1.97 1.97 Cyclohexane, g 70 70 CuCl₂•2H₂O, g 1.624 — Water, g 4.774.77 Ascorbic Acid, g — 1.299 Water/Surfactant Ratio 22.54 21.03

In the experiments of Examples 7 and 8, the ascorbic acid microemulsionwas poured, through a funnel, into the Cu (II) microemulsion. The bluecolor was discharged and a water white reaction mixture, with no visiblesolid, was observed in each case. After one month's storage in opaquebottles, the product of Example 7 consisted of suspended white solid andwater white liquid. In that of Example 8 the white solid had settled.

TEM was performed as described above. Particle size of the nanosizedCuCl from Example 7 (w=14-15) was 6.67±4.65 nm and of Example 8(w=21-22.5) was 5.66±1.70 nm. XRD of the solid from Example 8 confirmedthat it was CuCl. Average particle size of the CuCl, determined from theXRD pattern by the Debye-Scherrer method, was 92 nm.

The present invention provides nanosized copper (I) compounds, andmethods of making them, that are useful in catalytic, electronic,magnetic, and coating applications. The method the present inventionprovides a simple method of making the nanosized copper (I) compoundsutilizing reverse micelles or microemulsions with selective reduction ofthe copper (II) precursor to the desirable copper (I) nanosizedcompound.

While the present invention has been particularly described, inconjunction with specific preferred embodiments, it is evident that manyalternatives, modifications, and variations will be apparent to thoseskilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives, modifications, and variations as falling within the truescope and spirit of the present invention.

1. A method of preparing nanosized copper (I) cyanide comprising the steps of: providing a first microemulsion having a polar phase to surfactant molar ratio of less than about 30 comprising: a low or non-polar continuous phase comprising a surfactant, and a discontinuous polar phase comprising a copper (II) precursor wherein the discontinuous polar phase comprises nanosized droplets of the copper (II) precursor; providing a second microemulsion having a polar phase to surfactant molar ratio of less than about 30 comprising: a low or non-polar continuous phase comprising a surfactant, and a discontinuous polar phase comprising a cyanide salt soluble in the polar phase wherein the discontinuous polar phase comprises nanosized droplets of the cyanide salt; combining the first and second microemulsions to form copper (II) cyanide; thermally decomposing the copper (II) cyanide to copper (I) cyanide; and collecting the nanosized copper (I) cyanide having an average particle size of less than 100 nanometers.
 2. The method of claim 1 wherein the non-polar phase comprises a compound selected from the group consisting of an alkane, an alkylated benzene and a cyclic siloxane.
 3. The method of claim 1 wherein the non-polar phase comprises a cyclic siloxane having the general formula (RR′SiO)_(n) wherein R and R′ are independently selected from the group consisting of methyl, ethyl, phenyl and phenethyl, and n is 3 to
 30. 4. The method of claim 1 wherein the non-polar phase comprises a cyclic siloxane having the formula (RR′SiO)_(n) wherein R and R′ are both methyl and n is
 4. 5. The method of claim 1 wherein the surfactant is a non-ionic surfactant comprising an alkylphenolalkoxylate.
 6. The method of claim 1 wherein the surfactant is a cationic surfactant comprising an alkyl ammonium salt.
 7. The method of claim 6 wherein the cationic surfactant is hexadecyltrimethylammonium bromide.
 8. The method of claim 1 wherein the surfactant is an anionic surfactant selected from the group consisting of sodium dodecylsulfate and sodium bis(2-ethylhexyl)sulfosuccinate.
 9. The method of claim 1 wherein the surfactant is a zwitterionic surfactant selected from the group consisting of 3-(dimethyldodecyl-ammonium)propane sulfonate and cetyltrimethylammonium p-toluene sulfonate.
 10. The method of claim 1 wherein the copper (II) precursor comprises CuCl₂ in an aqueous solution.
 11. The method of claim 1 wherein the cyanide salt is KCN. 